This invention relates to liquid fertilizers and organophosphorus pesticides. In particular, this invention relates to improved compositions for use in combining emulsifiable organophosphorus pesticide concentrates with aqueous fertilizer solutions for simultaneous field application.
An emulsifiable concentrate is a formulation of a chemical pesticide which is commonly used when the latter is intended for dilution at the field site. The formulation consists of a solution of the pesticide in a water-immiscible or partially water-miscible solvent which forms an emulsion upon dilution with water. Typical solvents include mineral oils, petroleum solvents, chlorinated hydrocarbons, alcohols, glycols, ethers, esters, and ketones. A surface active compound is frequently included in the concentrate to promote emulsification and emulsion stability.
An emulsifiable concentrate has an advantage over solid or semi-solid pesticide formulations in that it is a liquid and can thus be easily mixed with a liquid fertilizer so that the two can be applied to the field at the same time in a common piece of apparatus. Common fertilizer application equipment can be used to distribute a mixture containing both the fertilizer, preferably dissolved in water, and the emulsifiable pesticide concentrate, at prescribed dilution. Both fertilization and insect control are thereby achieved by a single application.
Among the liquid fertilizers in current use are those commonly known as "N-P" and "N-P-K" fertilizers. As their designations indicate, these fertilizers are identified by numbers corresponding to the relative quantities of nitrogen, phosphorus, and potassium salts, expressed as N, P.sub.2 O.sub.5, and K.sub.2 O, respectively. Unfortunately, certain fertilizers when combined with the pesticide produce an emulsion of low stability. Sometimes, agitation inherent in the application equipment compensates for this. Tractors with spray booms, for example, which are used for broad area application, provide agitation through the pumps which feed the booms and the pump recycle lines which control the spray rate. Additional agitation is provided by paddles in the spray tanks of some tractors. Further agitation is achieved during the transfer of the fertilizer from the nurse tank in which it is brought to the field to the tractor spray tank in which it is combined with the pesticide mixture.
Each of these types of agitation helps to keep the dispersed phase from settling out of the pesticide-fertilizer emulsion. Unfortunately, these devices are not always sufficient to prevent the mixture from separating. When separation occurs, the result is an uneven application of the pesticide over the field. Equipment failure may also result as the feed lines become clogged with thick portions which have separated from the mixture. The problem is more pronounced, of course, when equipment containing no agitation mechanism is used.
The problem becomes particularly acute when fertilizer, pesticide, and crop seeds are placed in the soil simultaneously or in close succession. It is a common practice to use a simple piece of planting apparatus, such as a corn planter, to dig a furrow, deposit a row of seeds therein, and place a fluid mixture containing the pesticide and a high potency fertilizer in parallel bands on either side of the seeded row. This is commonly referred to as "split-boot" application. A fertilizer of relatively high salt content, commonly referred to as a "starter" fertilizer, is used to provide an extra impetus to initiate crop growth. The pesticide meanwhile serves to control insects which attack the seeds and seedlings. Unlike tractors equipped with pumps and boom sprayers for broad area application, many planters have no inherent agitation beyond that provided by the normal jostling which occurs as they proceed across the field. The fluid mixture is often fed to the soil by a squeeze pump which is driven by the tractor wheels, providing very little agitation. Separation of the pesticide suspension can occur readily in such an apparatus. In addition, the fertilizer itself tends to promote separation, because emulsion stability generally decreases with increasing fertilizer salt content.